Effects of the delta-isobar (∆) mixing on the spin-isospin response functions in finite nuclei are studied in the quasi-elastic region.A method to calculate the response function for a finite system composed of nucleon (N ) and ∆ is formulated in a ring approximation. It is designed to treat the ∆-related Landau-Migdal parameters, g ′ N ∆ and g ′ ∆∆ , and the nucleon parameter g ′ N N , independently, so that the universality ansatz,